Better absolute path handling (#19727)

Closes #19866

This PR supersedes #19228, as #19228 encountered too many merge
conflicts.

After some exploration, I found that for paths with the `\\?\` prefix,
we can safely remove it and consistently use the clean paths in all
cases. Previously, in #19228, I thought we would still need the `\\?\`
prefix for IO operations to handle long paths better. However, this
turns out to be unnecessary because Rust automatically manages this for
us when calling IO-related APIs. For details, refer to Rust's internal
function
[`get_long_path`](017ae1b21f/library/std/src/sys/path/windows.rs (L225-L233)).

Therefore, we can always store and use paths without the `\\?\` prefix.

This PR introduces a `SanitizedPath` structure, which represents a path
stripped of the `\\?\` prefix. To prevent untrimmed paths from being
mistakenly passed into `Worktree`, the type of `Worktree`’s `abs_path`
member variable has been changed to `SanitizedPath`.

Additionally, this PR reverts the changes of #15856 and #18726. After
testing, it appears that the issues those PRs addressed can be resolved
by this PR.

### Existing Issue
To keep the scope of modifications manageable, `Worktree::abs_path` has
retained its current signature as `fn abs_path(&self) -> Arc<Path>`,
rather than returning a `SanitizedPath`. Updating the method to return
`SanitizedPath`—which may better resolve path inconsistencies—would
likely introduce extensive changes similar to those in #19228.

Currently, the limitation is as follows:

```rust
let abs_path: &Arc<Path> = snapshot.abs_path();
let some_non_trimmed_path = Path::new("\\\\?\\C:\\Users\\user\\Desktop\\project"); 
// The caller performs some actions here:
some_non_trimmed_path.strip_prefix(abs_path);  // This fails
some_non_trimmed_path.starts_with(abs_path);   // This fails too
```

The final two lines will fail because `snapshot.abs_path()` returns a
clean path without the `\\?\` prefix. I have identified two relevant
instances that may face this issue:
-
[lsp_store.rs#L3578](0173479d18/crates/project/src/lsp_store.rs (L3578))
-
[worktree.rs#L4338](0173479d18/crates/worktree/src/worktree.rs (L4338))

Switching `Worktree::abs_path` to return `SanitizedPath` would resolve
these issues but would also lead to many code changes.

Any suggestions or feedback on this approach are very welcome.

cc @SomeoneToIgnore 

Release Notes:

- N/A

crates/gpui/src/platform/windows/platform.rs

@@ -6,7 +6,7 @@ use std::{
     sync::Arc,
 };
 
-use ::util::ResultExt;
+use ::util::{paths::SanitizedPath, ResultExt};
 use anyhow::{anyhow, Context, Result};
 use async_task::Runnable;
 use futures::channel::oneshot::{self, Receiver};
@@ -645,13 +645,11 @@ fn file_save_dialog(directory: PathBuf) -> Result<Option<PathBuf>> {
     let dialog: IFileSaveDialog = unsafe { CoCreateInstance(&FileSaveDialog, None, CLSCTX_ALL)? };
     if !directory.to_string_lossy().is_empty() {
         if let Some(full_path) = directory.canonicalize().log_err() {
-            let full_path = full_path.to_string_lossy();
-            let full_path_str = full_path.trim_start_matches("\\\\?\\");
-            if !full_path_str.is_empty() {
-                let path_item: IShellItem =
-                    unsafe { SHCreateItemFromParsingName(&HSTRING::from(full_path_str), None)? };
-                unsafe { dialog.SetFolder(&path_item).log_err() };
-            }
+            let full_path = SanitizedPath::from(full_path);
+            let full_path_string = full_path.to_string();
+            let path_item: IShellItem =
+                unsafe { SHCreateItemFromParsingName(&HSTRING::from(full_path_string), None)? };
+            unsafe { dialog.SetFolder(&path_item).log_err() };
         }
     }
     unsafe {